Not getting full RPMs

Gordon J · Oct 19, 2018

Last June hauled the boat and painted bottom. On way back to Marina I was able to get full rpms and speed or of my twin Cummins 330s. 2800 rpms at 15 knots.

Today I put the boat back in the water after hauling for hurricanes and can get only 2650 - 2700 rpms and 12 knots. Between the two events I disassembled and cleaned racor 1000s. There is some kind odd check ball/valve on the racor. Any chance a mis install could be causing my issue?

Thanks for thoughts suggestions?

Thanks
Gordon

C lectric · Oct 19, 2018

Don't know if that check ball would have caused this but there is a right and a wrong way to install the seat it 'seats' on. THere is printing indicating orientation and done incorrectly it can cause trouble.
Mike Negley has written many times about this seat and the need for attention to orientation.

Do you have a vacuum guage on the engine side of the filters? If not they can often help troubleshoot. You just want one with the telltale needle which stays at the highest reading achieved so you don't need to watch it.

Racor offers one as does Designated Engineer, a better one but needs some more fittings usually.
If you have any kind of fuel restriction that will limit power from the engines.

One question when you were down on power/speed, were you getting ANY BLACK OR DARK SMOKE?

If no dark smoke that usually means a fuel supply problem. If there is dark smoke that usually means an air restriction or overload for what ever reason.

DavidM · Oct 19, 2018

The following are probably more common reasons for low power/rpms:

1. Fouled bottom or prop.
2. Corroded turbo exhaus throat due to water intrusion from exhaust.

To check for #2, pull off the exhaust from the turbo and look inside. Any pitting or rust spots is a sure sign of sea water corrosion.

David

cafesport · Oct 19, 2018

Sounds like you may have installed the check valve gasket upside down which is easy to do if you don’t follow racor’s instructions. The lip goes up and the ball needs to sit on the flat edge of the seal not the dished edge. Very counterintuitive.

Gordon J · Oct 19, 2018

Thanks for the reply. Favor vacuum gauges read near zero. At max rpm lots of grey smoke, when running normal rpms no smoke

Gordon J · Oct 19, 2018

Not bottom

djmarchand said:
The following are probably more common reasons for low power/rpms:

1. Fouled bottom or prop.
2. Corroded turbo exhaus throat due to water intrusion from exhaust.

To check for #2, pull off the exhaust from the turbo and look inside. Any pitting or rust spots is a sure sign of sea water corrosion.

Thanks David. New exhaust risers two years ago. They are built so even if they leaked water would go to muffler. Just came from the yard. Bottom is clean as is the running gear.

High Wire · Oct 19, 2018

So what changed?
Disassembly and re-assembly of Racor.
Boat hauled and blocked.
Boat splashed back in water.
Anything else? Bought fuel, bumped bottom, air intakes clogged, tank vent clogged, etc?

Affects BOTH engines?

9 of 10 its the Racor somehow.
Do you have a second racor with a selector? If so, valve in second racor and test run.

DavidM · Oct 19, 2018

Gordon J said:
djmarchand said:

Thanks David. New exhaust risers two years ago. They are built so even if they leaked water would go to muffler. Just came from the yard. Bottom is clean as is the running gear.

Click to expand...

Exhaust risers failing and leaking salt water back into the turbo are a lesser concern. I appreciate that yours will drain down to the muffler if it fails. The more prevalent problem is sea water backing up from the transom exhaust and getting back into the turbo.

David

Brooksie · Oct 19, 2018

The Racor ball is hollow aluminum and floats on water closing off the passage. I doubt that is your problem. Although it's funny both engines are affected the same, first completely bleed your system up to and including each injector.

Could be that when the hauled the boat they tipped it bow down so water flowed into the engines. I happens but I hope not to you.

OldDan1943 · Oct 19, 2018

Brooksie said:
The Racor ball is hollow aluminum and floats on water closing off the passage. I doubt that is your problem. Although it's funny both engines are affected the same, first completely bleed your system up to and including each injector.

Could be that when the hauled the boat they tipped it bow down so water flowed into the engines. I happens but I hope not to you.

Check the oil for signs of water, drain the muffler.

Gordon J · Oct 20, 2018

Still no issue

djmarchand said:
Gordon J said:

Exhaust risers failing and leaking salt water back into the turbo are a lesser concern. I appreciate that yours will drain down to the muffler if it fails. The more prevalent problem is sea water backing up from the transom exhaust and getting back into the turbo.

David

Click to expand...

I cant imagine a scenario on this noat that would make that possible. Thanks for brainstorming with me.

Gordon

Gordon J · Oct 20, 2018

Ski, you there?

Any ideas?

Gordon

twistedtree · Oct 20, 2018

cafesport said:
Sounds like you may have installed the check valve gasket upside down which is easy to do if you don’t follow racor’s instructions. The lip goes up and the ball needs to sit on the flat edge of the seal not the dished edge. Very counterintuitive.

OK, you guys have me going here. I was unaware of any check valve in the Racor filters. Where and why? Are we talking about Racor 500, 900, 1000 filters or maybe something else?

cafesport · Oct 20, 2018

Peter all three have them to prevent the fuel from draining back to the supply side resulting in loss of prime. Here’s a nice article that explains it

http://www.racornews.com/single-post/2016/1/25/Mythbusters-Fuel-Filters

*And a brief excerpt for those who can’t access the link.

UNFILTERED THINKING
*
The first misunderstanding about fuel filters revolves around the ball. Many believe the ball serves

*
as a check valve to keep water from going up into the filter element. As the theory goes, the ball is plastic and floats, blocking water. In fact, the ball is aluminum, doesn’t float, and has nothing to do with water.
*

The engineers put it there to prevent fuel from draining out of the filter and back into the supply line when the engine is shut off. The flow of fuel back toward the tank pushes the ball into a seat, acting as a check valve to stop the flow. In some applications, such as when the filter has been installed below the tank pick up, this back flow would not be a concern. But in many applications the filter can be at the high point, and fuel running back to the tank can easily lead to a loss of prime.

twistedtree · Oct 20, 2018

cafesport said:
Peter all three have them to prevent the fuel from draining back to the supply side resulting in loss of prime. Here’s a nice article that explains it

Mythbusters: Fuel Filters | Racor News

*And a brief excerpt for those who can’t access the link.

UNFILTERED THINKING
*
The first misunderstanding about fuel filters revolves around the ball. Many believe the ball serves

*
as a check valve to keep water from going up into the filter element. As the theory goes, the ball is plastic and floats, blocking water. In fact, the ball is aluminum, doesn’t float, and has nothing to do with water.
*

The engineers put it there to prevent fuel from draining out of the filter and back into the supply line when the engine is shut off. The flow of fuel back toward the tank pushes the ball into a seat, acting as a check valve to stop the flow. In some applications, such as when the filter has been installed below the tank pick up, this back flow would not be a concern. But in many applications the filter can be at the high point, and fuel running back to the tank can easily lead to a loss of prime.

Cool, you learn something new everyday - hopefully. I never knew that was there.

Gordon J · Oct 21, 2018

Thanks for taking

cafesport said:
Peter all three have them to prevent the fuel from draining back to the supply side resulting in loss of prime. Here’s a nice article that explains it

Mythbusters: Fuel Filters | Racor News

*And a brief excerpt for those who can’t access the link.

UNFILTERED THINKING
*
The first misunderstanding about fuel filters revolves around the ball. Many believe the ball serves

*
as a check valve to keep water from going up into the filter element. As the theory goes, the ball is plastic and floats, blocking water. In fact, the ball is aluminum, doesn’t float, and has nothing to do with water.
*

The engineers put it there to prevent fuel from draining out of the filter and back into the supply line when the engine is shut off. The flow of fuel back toward the tank pushes the ball into a seat, acting as a check valve to stop the flow. In some applications, such as when the filter has been installed below the tank pick up, this back flow would not be a concern. But in many applications the filter can be at the high point, and fuel running back to the tank can easily lead to a loss of prime.

Thanks for taking the time to explain. I can scratch this issue of my list. Even if wrongly installed Racors are lower than tank pick up.

Gordon

kapnd · Oct 21, 2018

Cables are known to stretch, limit screws sometimes move, so go through the control system, possibly remove cable at throttle lever and turn by hand to verify top rpms.

Vashon_Trawler · Oct 22, 2018

I learned that it doesn't take much to decrease one's WOT RPM. I recently experienced a 200 RPM drop in WOT. I replaced all of my fuel filters and a few fuel lines that were due for replacement, changed the air filter, verified the bottom was clean, etc. My prop received a few coats of bottom paint a year or so ago, which was beginning to flake off in large areas. Combined with some barnacle remnants, I suspected the prop was the issue. I had the prop pulled, cleaned, and dynamically balanced; I used the Velox system for anti-fouling. I now achieve 3600 RPM at WOT, which is 200 RPM over my previous "normal" WOT of 3400--400 RPM over where I was prior to the prop being pulled.

A side note on the prop... My prop is a 16x8 bronze Chinese made Hung-Shen HTP-3 heavy thrust. The prop shop said it was "all over the place" and needed balancing--poor quality control I guess.

Gordon J · Oct 22, 2018

Ok, i am going to tell on myself. Of course the problem was easy, and i am kicking myself in the tail. My trim tabs did not deploy. Why, one might ask?. I failed to flip the circuit breaker to on. I thought i did not feel the bow go down because we were going so slow. I was wrong. Once trim tabs engaged, she was back to normal.

Gordon

Mrdi · Oct 26, 2018

Embarrassingly cheap, great resolution.

firehoser75 · Oct 26, 2018

Hi Gordon,
Even though you "solved your issue", and I have had similar "brain farts", you might want to check out sbmar.com. It is a website run by Seaboard Marine in California, but Tony posts tons and tons of free, really good information, particularly for Cummins engines (which I have , 6BTA). At wide open throttle, you should really aim for about 2950 rpm. Check out his site, he explains why way better than I could, and describes the full process to check this out properly.

Regards,
Tom

Gordon J · Oct 26, 2018

Thanks Tom. I have been to his site plenty and subscribed to boat diesel when Tony was moderator. I’ll go back and look, but the manual calls for 2800 top rpm.

Gordon

markpierce · Oct 26, 2018

I rarely operate, even briefly, at wide-open throttle [2400 RPM] (usually operate at 43% [1800 RPM] load and occasionally at 72% [2200 RPM]. The only time max RPM wasn't achieved was when the fuel filter needed replacement.

Not getting full RPMs

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